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PubMedDate not supplied

[Pyruvate and glucose transport through the erythrocyte membranes and the role of spectrin in these processes].

Effect of antibody to peripheral protein spectrin and antibody to integral protein of band 3 on kinetic parameters of pyruvate and glucose transport in the pink erythrocyte ghosts has been studied. It is shown that spectrin structure reorganization induced by the antibody to this protein has different effect on pyruvate and glucose transport parameters. Band 3 protein modification with the help of the antibody to this protein changes pyruvate transport parameters, while glucose transport is not changed. The data obtained show that facilitated diffusion of glucose and anions in the erythrocyte membrane is carried out by different carriers, the action of these carriers essentially depending on the structure state of spectrin.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1984

[Amino acid transfer at the fetal surface of the trophoblast and the characterization of its carrier in the rat placenta in vivo].

A new technique for injecting tracer into the rat fetus in utero, intraperitoneally, was employed to characterize the amino acid exchange at the fetal surface of the trophoblast and to study the transplacental amino acid transfer. Calculation of tissue fluid distribution via 3H-inulin space made it possible to estimate the placental intracellular amino acid concentration on the basis of the cord and maternal plasma concentration. The fetal plasma free amino acid was taken up at a considerable rate by the fetal surface of the placenta in umbilical circulation. The amino acid from fetal plasma was utilized for the protein synthesis and deamination in the placenta. It was speculated that the amino acid transfer at the fetal surface of the placenta was carrier-mediated facilitated diffusion, not simple diffusion, on the basis of the data showing the stereospecificity for the isomers. From these results it was considered that the fetal, not maternal, plasma free amino acid concentration greatly influenced the fetal amino acid net uptake.

Alanine↗
PubMed1984

Permeation of long-chain fatty acid into adipocytes. Kinetics, specificity, and evidence for involvement of a membrane protein.

This study extends our earlier work (Abumrad, N. A., Perkins, R.C., Park, J.H., and Park, C.R. J. Biol. Chem. 256, 9183-9191) which showed that oleate permeates the plasma membrane of the rat adipocyte principally by a transport process with the characteristics of facilitated diffusion. In the present study, fatty acid (FA) transport is characterized with regard to its specificity and susceptibility to inhibition by protein modifiers. The kinetics of competitive inhibition for transport of oleate and stearate are shown under conditions where complications due to competition for binding of FAs to the albumin in the medium are minimized. Stearate inhibits influx of tracer oleate with a Ki that closely approximates its Km and, conversely, oleate inhibits similarly the influx of tracer stearate. Specificity of the FA transport system is shown in studies using a variety of natural FAs of different chain length, or FA analogues. Oleate (Km = 0.06 microM), stearate (Km = 0.16 microM), linoleate (Km = 0.22 microM), palmitate, (Km = 0.2 microM), and laurate (Km = 1.5 microM) are good substrates, but octanoate is not transported. An oxazolidine ring on C-5 but not on C-16 of stearate blocks binding to the transporter. Methylation of the carboxyl function but not alpha-bromination inhibits transport. These studies suggest that a FA must have a hydrocarbon chain of at least nine carbons and a free carboxyl function to be recognized by the transporter. FA transport does not require Na or ATP. Pronase but not trypsin treatment of intact cells reduces fatty acid influx. Transport is insensitive to maleimides. It is strongly and irreversibly blocked by pretreatment of the cells with the stilbene compounds, 4,4'-diisothiocyanostilbene-2,2'-disulfonate and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, but only slightly inhibited by dipyridamole. Polyacrylamide gel electrophoresis of plasma membrane proteins from cells treated with [3H] 4,4'-diisothiocyanostilbene-2,2'-disulfonate shows a peak of radioactivity at about Mr = 85,000. When cells are incubated in various concentrations of this agent, the counts recovered in the peak reach a maximum coincident with maximum inhibition of transport. We conclude that permeation of the plasma membrane of the adipocyte by long-chain FAs at physiological concentrations is mediated by a protein transporter with distinct specificity requirements.

Adipose Tissue↗
PubMed1982

Effect of nafenopin on the uptake of bilirubin and sulfobromophthalein by isolated perfused rat liver.

Hepatic uptake of bilirubin and sulfobromophthalein has kinetic characteristics suggesting facilitated diffusion. Because these compounds demonstrate mutual competition for uptake, a shared uptake mechanism has been presumed. Previous studies in isolated perfused regenerating liver revealed depressed uptake of bilirubin, sulfobromophthalein, and asialoorosomucoid, a desialylated glycoprotein which enters hepatocytes by receptor-mediated endocytosis. This study was designed to determine whether or not depressed transport seen in liver regeneration occurs in other states of hepatocellular proliferation. Rats were pretreated with nafenopin (200 mg/kg . day x 2), a drug that causes rapid hepatocellular proliferation similar to that seen in regeneration. Twenty-four hours after nafenopin treatment, liver weight increased by 40%. Influx, efflux, and sequestration rate constants in isolated perfused liver were quantitated by a computer fit to the model of Goresky. Results 1 day after nafenopin treatment revealed no change in transport parameters for bilirubin and asialoorosomucoid, but 55% and 49% reductions in influx of sulfobromophthalein and conjugated bilirubin, respectively. These studies suggest that hepatocellular proliferation alone is not responsible for the transport alterations seen during liver regeneration. Nafenopin effectively unmasks differences in uptake of bilirubin and other more water soluble organic anions such as sulfobromophthalein and conjugated bilirubin, suggesting that their uptake mechanisms are partially independent.

Animals↗
PubMed1983

Biochemical functions of magnesium.

Magnesium is required by many enzymes as a co-factor and may couple primarily with the enzyme or the substrate in different reactions. Free cytosolic magnesium affects cell energy, the action of various hormones on target cells, protein synthesis and cellular electrolyte content. Magnesium enters the cell by a process of facilitated diffusion requiring a transporter, and leaves it by an active process utilizing adenosine triphosphate.

Cells↗
PubMed1981

Action of clinically utilized 5-nitroimidazoles on microorganisms.

Various nitroimidazoles are used as antimicrobial and radiosensitizing agents in human medicine. Of these, 5-nitroimidazoles show high selective toxicity for anaerobic prokaryotes and eukaryotes. This review discusses the effects of 5-nitroimidazoles on microorganisms, i.e. microbicidal action, radiosensitizing action, inhibition of photosynthetic microorganisms, and induction of mutations. All these actions are enhanced by anaerobiosis and inhibited by aerobiosis or by the presence of certain reducible compounds. There is no indication that antimicrobial action could be dissociated from mutagenic properties. Relative resistance to 5-nitroimidazoles has been detected in some isolates of Bacteroides fragilis and Trichomonas vaginalis and was experimentally developed in B. fragilis and various trichomonads. Nitroimidazoles enter the microorganisms by diffusion. Facilitated transport has not been detected. The compound is reduced by low oxidation-reduction potential ferredoxin and similar electron transport components in the cell. In microorganisms highly susceptible to metronidazole, such compounds play a significant metabolic role. The reduction increases the outside-inside concentration gradient and thus drives further uptake. Certain short-lived products of the reduction are responsible for the cytotoxic action. In less susceptible organisms only limited amounts of such products are formed, and thus the cells are not killed but may undergo mutations. A major component of cytotoxicity is damage to DNA but other mechanisms cannot be excluded at present.

Anaerobiosis↗
PubMed1981

Plasmid-determined resistance to tetracycline.

A general concept is proposed to explain the mechanism of bacterial resistance to tetracycline, and is essentially based on experimental date and a review of recently of recently published studies. It is assumed that tetracyclines are accumulated in the bacterial cell by an energy-demanding, carrier-mediated influx-mechanism, at a rate depending on the concentration of the antibiotic in the medium. Tetracyclines seep out of the cell by facilitated diffusion at a rate depending on the concentration inside the cell. At steady state, when no net alteration of the intracellular concentration is evident, the molecules of the antibiotic, inside and outside the cell, are exchanged by influx and efflux. In the resistant organism, an additional energy-demanding and carrier-mediated efflux-mechanism is assumed. The total efflux rate is therefore increased, and the steady state is obtained at a lower intracellular level of tetracyclines. It is possible that, in addition, the influx is decreased in the resistant organism.

Bacteria↗
PubMed1978

Mechanism of natural resistance of rat ascites hepatomas to 1-beta-D-arabinofuranosylcytosine.

The biochemical basis for natural resistance to 1-beta-D-arabinofuranosylcytosine (ara-C) was investigated in the intact cells of 4 rat ascites hepatomas, AH-66F, AH-60C, AH-109A, and AH-66, whose sensitivity to ara-C was different in that decreasing order. The initial rapid uptake of ara-C, mediated by the facilitated diffusion, was similar in all the cell lines tested but the subsequent slow uptake due to phosphorylation of ara-C was inversely correlated with their drug resistance. The capacity for drug phosphorylation was slightly higher in AH-66F and much lower in AH-60C, AH-109A, and AH-66 than in the host bone marrow. In contrast, mouse leukemia L-1210, one of the tumors sensitive to ara-C, phosphorylated the drug about 7 times faster than AH-66F and 4 times faster than the host bone marrow. More than 95% of phosphorylated ara-C was the triphosphate, the active form. Deamination of ara-C was not observed in any tumor or bone marrow. It is concluded that the low capacity for nucleotide formation is related to the natural resistance of rat ascites hepatomas to ara-C.

Animals↗
PubMed1982

Transport of pyridoxine and pyridoxal 5'-phosphate in isolated rat liver mitochondria.

The transport of [14C]pyridoxal-P and [14C]pyridoxine into isolated rat mitochondria was studied by centrifugal filtration. The incubation medium contained 20 mM 2-oxoglutarate and 10 mM inorganic phosphate to inhibit metabolism of pyridoxal-P by the mitochondria. The ratio of [14C]pyridoxine space to [3H]H2O space rapidly attained unity independent of the [14C]pyridoxine concentration in the medium and remained unchanged for up to 90 min of incubation. These data suggest simple passive diffusion for the transport of pyridoxine into the mitochondria. By contrast, the ratio of [14C]pyridoxal-P space to [3H]H2O space rose rapidly to exceed 1 in the first 15 min and continued to rise at a slower rate for as long as it was measured. The accumulation of [14C]pyridoxal-P was not decreased by inhibitors and uncouplers of oxidative phosphorylation. Fractionation of the mitochondria with digitonin revealed that 19 and 340 pmol of [14C]pyridoxal-P/mg of protein were taken up by the mitochondria at 15 and 60 min of incubation, respectively. Most of the uptake in the first 15 min occurred in the intermembrane space, whereas the largest increase of [14C]pyridoxal-P between 15 and 60 min of incubation appeared in the matrix fraction. Significant binding of the [14C]pyridoxal-P to proteins in the two compartments was demonstrated by gel filtration. These data indicate that pyridoxal-P can rapidly enter the intermembrane space of isolated mitochondria, but its penetration into the matrix occurs at a slower and more sustained rate (i.e. 9-16 pmol/h/mg of protein). It is concluded that the transport of pyridoxal-P into isolated rat liver mitochondria is energy-independent and is most consistent with passive diffusion facilitated by protein binding once this coenzyme enters the different compartments of the mitochondria.

Animals↗
PubMed1981

Transport and metabolism of pyridoxine in rabbit iris--ciliary body.

Isolated rabbit iris--ciliary body preparations were found to accumulate 3H-pyridoxine by a mechanism that was time- and temperature-dependent, saturable in part, but not altered by omission of oxygen or specific ions. Tissue accumulation was only partially energy-dependent, and metabolic inhibitors had only small effects. Other B6 vitamers markedly blocked accumulation. Metabolism of 3H-pyridoxine within the tissue was extensive. After 60 min incubation with 3H-pyridoxine, about 65% of the radioactivity in the iris--ciliary body was associated with phosphorylated vitamers which did not efflux from the tissue as readily as did the nonphosphorylated forms. Unaltered pyridoxine accounted for only 16% of intracellular 3H-B6, and this did not represent accumulation against a concentration gradient. A similar saturable uptake process occurred in vivo. These data were consistent with the hypothesis that pyridoxine was accumulated by facilitated diffusion with intracellular trapping of phosphorylated metabolites.

Animals↗
PubMed1980

[D-xylose transport in cultured mammalian cells].

The uptake of D-xylose by CHO-K1 cells in monolayer conditions, and by suspended L- and HeLa cells has been studied. The initial velocity is a function of exogenous xylose concentration. The estimated kinetic constants, Km and Vmax, at 37 degrees were, resp., 20 mM and 10 mmol/min for CHO cells, 12.5 mM and 2.8 mmol/min for L-cells, and at 16 degrees--3 mM and 2.6 mmol/min for HeLa cells. The transport of D-xylose was inhibited by D-glucose and phlorizin. It is concluded that D-xylose may penetrate into the cells by a passive transport (facilitated diffusion), and that D-xylose may be used as a transport analogue of D-glucose. The intracellular H2O space, determined from the equilibrium level of D-xylose for the monolayer of CHO cells was equal to 1.5 microliter on 10(6) cells.

Animals↗
PubMed1980

[Membrane transport of antineoplastic drugs and its relevance to tumour chemotherapy (author's transl)].

The permeation of cell membranes by several antineoplastic drugs (AD) exhibits characteristics of carrier-mediated transport processes (facilitated diffusion or active transport); the main representatives among these AD are mechlorethamine, cyclophosphamide, melphalan, methotrexate, 6-mercaptopurine, 5-fluorouracil, cytarabine, 5-fluorodeoxyuridine, vincristine, vinblastine, adriamycin, daunorubicin and dactinomycin. Inhibition or stimulation of the membrane transport of AD influences absorption, distribution, elimination, therapeutic effectiveness and toxicity. The choice of certain combination therapies may increase the selectivity of AD by influencing membrane transport. A change in the properties of transport systems is one possible reason for the resistance of tumour cells to various AD.

Animals↗
PubMedDate not supplied

Zinc cellular traffic: physiopathological considerations.

Zinc cellular traffic is reviewed in both influx and efflux stages. Zinc influx happens through three different modalities: 1) anionic exchange channels, with the metal cotransported in complex form with anions, often as anionic monovalent complex (Zn [HCO3)2Cl]. Bicarbonate-ions, chloro-ions and thiocyanate-ions can stimulate zinc << uptake >>, while phosphate and sulphate-ions are inhibitory. 2) facilitated diffusion through amino acids which, by passing into cells, carry zinc (particularly cysteine and histidine) with them. 3) transferrin receptor route, very important for cellular uptake of iron and zinc. Various mitogenic factors cause increased synthesis of transferrin receptors and increase of metal uptake. Zinc efflux happens through zinc/calcium exchange (zinc efflux coupled with calcium influx). Calcium is then expelled from cells by means of calcium pump (with energy consumption), regulated by membrane Ca-ATPase. Impairment of this ionic exchange process may cause an intracellular accumulation (as may be seen in SHR rats).

Amino Acids↗
PubMed1995

Immunohistochemical localization of the glucose transporter GLUT1 in choroid plexus papillomas.

Normal chroid plexus tissue and five choroid plexus papillomas were examined with antibody specific for the glucose transporter GLUT1, one isoform of facilitated-diffusion glucose transporters, using the avidin-biotin-peroxidase complex (ABC) technique. GLUT1 in normal choroid plexus was localized at the basolateral plasma membrane of almost all epithelial cells. In three of five tumors, GLUT1 immunoreactivity was observed. A positive reaction was demonstrated at the plasma membrane of tumor cells. The number of GLUT1-positive cells was, however, much smaller than that of the normal choroid plexus. Our results suggest that GLUT1 expression in the choroid plexus is restrained during the course of transformation and that choroid plexus papilloma is composed of various differentiation tumor cells.

Adolescent↗
PubMed1994

L-fucose is accumulated via a specific transport system in eukaryotic cells.

L-Fucose is a monosaccharide normally present at low concentrations in serum and is the only levorotatory sugar utilized by mammalian systems. The metabolism of L-fucose is only partially understood. In this report, we characterize the uptake of L-fucose by four widely varying mammalian cell lines (murine neuroblastoma, bovine aortic endothelial, murine cerebral microvessel endothelial, and Madin-Darby canine kidney cells). Based on the criteria of saturability and specificity of L-fucose uptake, we conclude that L-fucose is accumulated via a specific recognition mechanism. Accumulation of L-fucose at 4 degrees C and in the presence of colchicine and cytochalasin D rules out receptor-mediated endocytosis as an uptake mechanism. Thus, the accumulation appears to be via a carrier system. Using a variety of criteria, we determined that L-fucose is not taken up by a glucose transporter system. Accumulation of L-[5,6-3H]fucose is Na(+)-independent and reduced by loading cells with L-fucose or depleting the cell of its phosphorylation capability, suggesting that the uptake of L-fucose is by passive facilitative diffusion. A significant amount of the L-fucose taken up by each of the four cell types was incorporated into protein and secreted into the medium.

Animals↗
PubMed1994

The importance of the creatine kinase reaction: the concept of metabolic capacitance.

The creatine kinase reaction is traditionally viewed as providing an energy reserve in muscle. However, the physiological importance of this reaction (and the analogous invertebrate reaction catalyzed by arginine kinase) is better understood when viewed as providing metabolic capacitance. This capacitance allows reduction of peak rates of ATP synthesis in cells that alternate between periods of high and low energy consumption. Furthermore, the capacitance allows repayment of energy "debt" that is incurred during periods of high energy demand to occur during periods of low rates of energy consumption. The creatine kinase reaction provides facilitated diffusion of ATP and ADP, which leads to spatial buffering in addition to temporal buffering. Data are presented which suggest that the existence of the creatine kinase reaction allows muscle cells to maintain reduced mitochondrial volume, support larger diameter fibers, and express faster isoforms of myosin. These data lead to speculation that there may be a coupling in the expression of metabolic and contractile proteins.

Animals↗
PubMed1993

Effects of carbon monoxide on isolated heart muscle cells.

By sequestering intracellular myoglobin of cardiac muscle cells in the nonfunctioning carboxymyoglobin form, carbon monoxide blocks myoglobin-facilitated diffusion of oxygen, as well as myoglobin-mediated oxidative phosphorylation. Here, we explore the hypothesis that the carbon monoxide blockade of myoglobin function may be responsible at the cellular level for a component of the cardiotoxicity of carbon monoxide observed during exercise. Suspensions of isolated rat cardiac myocytes were held in near steady states of oxygen pressure near the intracellular partial pressure of oxygen of the working heart (2 to 5 torr) and near the end-venous partial pressure of oxygen (20 torr). These suspensions were exposed to CO at low pressure (0.07 to 70 torr; 90 to 90,000 parts per million). The fraction of intracellular carboxymyoglobin, determined spectrophotometrically, was in good agreement with the fraction predicted from the ratio of carbon monoxide partial pressure to oxygen partial pressure. The effects observed were related to the fraction of intracellular myoglobin bound to CO. At physiological oxygen pressures no greater than 5 torr, after sequestration of approximately 50% of the myoglobin, steady-state oxygen uptake decreased significantly and was significantly less than the respiration of cell groups for which the fraction of carboxymyoglobin was 0% to 40%. When respiration is diminished, the rate of aerobic adenosine triphosphate synthesis (oxidative phosphorylation) also decreases. As in the whole heart, cytoplasmic adenosine triphosphate concentration in isolated heart cells is controlled at a constant level by the creatine phosphokinase equilibrium. When adenosine triphosphate utilization is unchanged, a sensitive monitor of the decreased adenosine triphosphate synthesis is the ratio of phophocreatine to adenosine triphosphate. When carboxymyoglobin was at least 40% of the total intracellular myoglobin, we found that the ratio of phosphocreatine to adenosine triphosphate in carbon monoxide-treated heart cells was significantly lower than that in control cells from the same preparation. Thus, we concluded that sequestering intracellular myoglobin as carboxymyoglobin significantly decreased the rate of oxidative phosphorylation of isolated cardiac myocytes. We estimate that intracellular myoglobin-dependent oxidative phosphorylation will be inhibited when approximately 20% to 40% of the arterial hemoglobin in the whole animal is carboxyhemoglobin.

Adenosine Triphosphate↗
PubMed1976

Selective advantages of various bacterial carbohydrate transport mechanisms.

At least four strategies have been developed by bacteria for capturing carbohydrates. They are typified by the transport mechanisms for glycerol, glucose, lactose, and galactose in Escherichia coli. Glycerol enters the cell by facilitated diffusion catalyzed by specific membrane protein. Once inside the cell, the substrate is trapped by phosphorylation mediated by an adenosine triphosphate (ATP)-dependent kinase. glucose is phosphorylated in transit by a membrane-associated phosphoenolpyruvate phosphotransferase system (PTS). A specific component of this complex serves also for signal recognition to chemotaxis. Lactose is concentrated chemically unaltered by beta-galactoside permease driven by a proton motive force. Galactose is also pumped into the cell, but the process is energized by ATP or its equivalent. In addition, there is a periplasmic galactose-binding protein essential for both transport and chemotactic response. The relative functional merits of each kind of transport mechanism are discussed. Although many bacterial species possess both the concentrative mechanism and the PTS, some employ the former and others the latter for beta-galactoside utilization. The postulate that the PTS is more avid in scavenging while the concentrative permease system permits a broader range of substrate exploitation is supported by the growth responses of 12 bacterial strains to several beta-galactosides.

Bacteria↗